1. Field of the Invention
The present invention relates to heat exchangers and, more particularly, to a heat exchanger with an increased heat transfer efficiency and a low-cost method of forming the heat exchanger.
2. Description of the Related Art
Telecommunications equipment is commonly housed in electronics cabinets that sit outside in residential and commercial neighborhoods. The cabinets are water tight and air tight to prevent water and dust from entering the cabinets and reducing the useful life of the equipment inside the cabinets.
When operating as intended, the telecommunications equipment produces heat which can damage the equipment when the heat inside the cabinet exceeds a predetermined temperature. To maintain an air tight enclosure and prevent the temperature from exceeding the predetermined temperature, electronics cabinets often use air-to-air heat exchangers.
FIGS. 1A–1C show views that illustrate a prior art air-to-air heat exchanger 100. FIG. 1A is a top plan view, FIG. 1B is a right side view, and FIG. 1C is a bottom plan view. As shown in FIGS. 1A–1C, heat exchanger 100 includes an air flow structure 110 that directs the flow of external and internal air through heat exchanger 100.
FIGS. 1D–1E show views that further illustrate air flow structure 110. FIG. 1D is a partial perspective view, and FIG. 1E is a partial plan view. As shown in FIGS. 1A–1E, air flow structure 110 has a top surface 112 and a bottom surface 114. In addition, structure 110 has a width W, a length L, a first end 116 that runs along the width W, and a second end 118 that runs along the width W.
In addition, air flow structure 110 includes a number of first grooves G1 that are formed in the top surface 112, and a number of second grooves G2 that are formed in the bottom surface 114. As shown, the first and second grooves G1 and G2 extend along the length L between the first and second ends 116 and 118.
Heat exchanger 100 also includes a number of first crimped ends 120 that close alternate ends of the second grooves G2 along the first end 116, and a number of second crimped ends 122 that close alternate ends of the first grooves G1 along the second end 118. In addition, a caulked region 123 is formed around each of the first and second crimped ends 120 and 122 to form an air tight seal.
As further shown in FIGS. 1A–1C, heat exchanger 100 also includes a first plate 124 that is formed adjacent to the top surface 112 of air flow structure 110. In the example, first plate 124 contacts the top surface 112, the first crimped ends 120, the second crimped ends 122, and the caulked regions 123 to form an air tight connection. In addition, first plate 124 has an external air inlet opening 126, and an external air exit opening 128. Opening 126 exposes a region adjacent to air flow structure 110, while opening 128 exposes the second grooves G2 of air flow structure 110.
Heat exchanger 100 further includes a second plate 130 that is formed adjacent to the bottom surface of 114 air flow structure 110. In the example, second plate 130 contacts the bottom surface 114, the first crimped ends 120, the second crimped ends 122, and the caulked regions 123 to form an air tight connection. Further, second plate 130 includes a base section 130A and sidewalls 130B that extend perpendicularly away from base section 130A to form an enclosure. The enclosure formed by base section 130A and sidewalls 130B is connected to first plate 124 to form an air tight connection.
Second plate 130 also has an internal air inlet opening 132, and an internal air exit opening 134. Opening 132 exposes a region adjacent to air flow structure 110, while opening 134 exposes the first grooves G1 of air flow structure 110.
As further shown in FIGS. 1A–1C, heat exchanger 100 includes an air flow generator 140, such as an axial fan, that is connected to first plate 124 adjacent to opening 126. Air flow generator 140 causes external air to follow a path 142 in through opening 126, along the second grooves G2, and out through opening 128.
Heat exchanger 100 additionally includes an air flow generator 144, such as an axial fan, that is connected to second plate 130 adjacent to opening 132. Air flow generator 144 causes internal air to follow a path 146 in through opening 132, along the first grooves G1, and out through opening 134.
In operation, a stream of internal cabinet air circulates through the telecommunications equipment, through opening 132 in second plate 130, and through the grooves G1. The stream of internal cabinet air continues through openings 134 in second plate 130 and back through the telecommunications equipment. As the internal cabinet air circulates, the internal cabinet air transfers heat to the skin of air flow structure 110.
At the same time, a stream of external air is pulled in from the outside through opening 126, and through grooves G2. The stream of external air continues through opening 128 and is exhausted without mixing with the internal cabinet air. The external air, which is cooler than the internal cabinet air, absorbs heat from the skin of air flow structure 110, thereby effecting a transfer of heat from the internal cabinet air to the external air.
One trend in the telecommunications industry is to make line replaceable cards such that, for example, a card that supports plain old telephone service (POTS) can be replaced with a card that supports both POTS and xDSL broadband data service. Replacement cards which provide more than basic POTS service, however, tend to generate more heat than basic POTS cards.
One problem with heat exchanger 100 is that it is difficult to increase the efficiency by which heat is transferred out of the cabinet. Thus, when a telecommunications cabinet is at or near its maximum heat capacity, it is difficult to replace basic POTS cards with cards that provide a wider variety of services without exceeding the maximum heat capacity of the cabinet.
One reason that it is difficult to increase the efficiency of heat exchanger 100 is that it is difficult to increase the number of grooves G1 and G2 per 2.54 centimeters (inch) beyond about two grooves per 2.54 centimeters (inch). FIGS. 1F–1H show perspective drawings that illustrate the fabrication of air flow structure 110.
As shown in FIG. 1F, to fabricate air flow structure 110, a corrugated air flow structure 150 is formed using conventional techniques. Next, as shown in FIG. 1G, alternate ends of air flow structure 150 are crimped to form crimped ends 120 and 122. The first and second plates 124 and 130 are attached to air flow structure 150. To prevent the internal cabinet air from mixing with the external air, the crimped ends 120 and 122 between the first and second plates 124 and 130 must be sealed. As shown in FIG. 1H, this is typically accomplished by hand applying a caulking material to the crimped ends 120 and 122 to form caulked regions 123.
However, to apply the caulking material, a significant amount of space is required to provide the access needed by the caulking gun. In addition, once the caulked regions 123 have been formed, the lateral spacing X between adjacent caulked regions 123 is relatively small. Thus, the small lateral space X between adjacent caulked regions 123 limits the number of grooves G1 and G2 that are available to approximately two per 2.54 centimeters (inch).
Heat exchanger 100 is also relatively expensive to fabricate. One reason for this is that the caulking material that is applied to the crimped ends 120 and 122 and the first and second plates 124 and 130 to formed caulked regions 123 is typically applied by hand. This, in turn, is a time consuming and expensive process. Thus, there is a need for a more efficient and less costly heat exchanger.